It is a well known principle of optical systems that a collimated beam of parallel light rays which enter a convex lens at separate points on the curved face of the lens will be brought to a focus at the focal point of the lens. As long as the collimated rays are nearly parallel to the optical axis, the image plane is in the vicinity of the focal point, regardless of where a ray enters the lens. Rotation of the collinated beam about the optical axis of the lens, does not move the focal point nor the image focused in a plane at the focal point. When a single optical channel system transmits such a beam as a single stream of data bits, the system is adequate as long as the data transmission rate requirements can be accommodated by such a system.
However, to facilitate the practical data transmission of present very high data rates, it is necessary to simultaneously transmit multiple parallel channels of data to provide the corresponding substantial increase in the rate of data transmission. Because it is necessary to separate the discrete parallel optical channels of data which are to be simultaneously transmitted, a multiple optical channel system may fail because it does not provide adequate means of optical channel separation.
An example of an application where such increased rates of data transmission occur, is in the transmission of video, audio or other data, between the multiple heads in a rotating scanner assembly and the stationary signal processing system, of a video or data tape recorder/reproducer. At present, such recorder/reproducers electromagnetic rotary transformers of very restricted tolerances and attendant substantial expense, as further discussed below.
Although fiber optic networks can be used to transmit multiple channels of data from a source, such source typically is stationary, and is normally a single or point source. To date, a practical fiber optic network which is operative with a multi-channel, rotary data source to provide high data rate transmission, is not available. Further, the known art has not solved the problem of adequate channel separation when transmitting multiple parallel channels of data generated by a rotating source utilizing simple geometric methods and generally available components.
The rotary optical coupler is a superior alternative to the rotary transformer in applications where the output generated by, for example, the magnetic head signals of the magnetic tape recorder/reproducer of previous mention, are converted to data bit streams for transmission to a receiving source, because of the significant advantage which the rotary optical coupler provides with respect to the less stringent mechanical tolerances when compared to the rotary transformer. Although the rotary transformer transmits multiple parallel channels of data, the potential for channel crosstalk in such a system requires substantially tight mechanical tolerances, achieved at considerable expense. The axial tolerance between the rotating and stationary elements of an optical coupler may be greater than 20 mils instead of less than the 1 mil tolerances required in a rotary transformer. Likewise, in an optical coupler, radial tolerances of the light sources and lens annuli may be on the order of .+-.5 mils, a readily attainable and inexpensive requirement.
Accordingly, it would be highly desirable to provide a multi-channel rotary coupler for data signal transmission which offers the advantages of substantial cost savings with a design of relative simplicity using readily available optical components, while generally retaining the speed and optical resolution of a fiber optic network.